Positive active material for secondary lithium battery, method for preparing the same and secondary lithium battery containing the positive active material

ABSTRACT

The present invention provides a positive active material for use in a secondary lithium battery, a method for preparing the positive active material and a secondary lithium battery containing the positive active material. The positive active material includes a core of lithium transition metal oxide represented by Formula LixMyN1-yO2-αAβ and a coating layer of lithium transition metal silicate represented by Formula x′Li2O.y′N′Oa.SiO2-λBζwhich in-situ formed on the core, wherein 0.8≤x≤1.3, 0.6≤y≤1.0, 0.01≤x′≤2.1, 0.2≤y′≤1.5, 0.1≤a≤3.0, 0≤α≤0.2, 0≤β≤0.4, 0≤λ≤0.5, 0≤ζ≤0.5. The positive active material according to the present invention has high capacity, desirable cycling performance and safety performance, as well as desirable thermal stability.

CROSS-REFERENCE TO RELATED APPLICATION

The present patent application claims the benefit of Chinese patentapplication number CN 201510074642.0 filed on Feb. 12, 2015, thecontents of which are hereby incorporated by reference.

BACKGROUND

The present invention generally relates to secondary lithium batteriesand, more particularly, to a positive active material having desirableperformances for secondary lithium battery and a method for preparingthe same.

DESCRIPTION OF RELATED ART

At present, positive active materials used in lithium ion batteriesgenerally include spinel structure LiM₂O₄ (M is Co, Ni, Mn et al.),layered lithium transition metal oxides LiMO₂ (M is Mn, Co, Ni et al)and olivine structure lithium phosphate salt LiMPO₄ (M is Fe, Mn, Co, Niet al). Layered lithium transition metal oxide LiCoO₂ is one of the mostpopular positive active materials in commercial applications due tosimple synthesis process and mature application technology. However, dueto high price of cobalt, toxicity of cobalt and poor safety performance,LiCoO₂ can hardly meet the actual requirements of large secondarylithium battery, especially cannot meet the requirements of powerbatteries which have high safety performances and a long cycle life. Toimprove the electrochemical performances of LiCoO₂, such as safetyperformance and cycling performance, it is proposed that coatingtreatment is applied to LiCoO₂. However, LiCoO₂ with coating treatmentstill cannot meet the requirements of actual use.

Layered lithium transition metal oxides represented by FormulaLiNi_(x)Co_(y)M_(1-x-y)O₂ is one of the latest positive active materialswhich have been widely used in lithium ion batteries due to low price,simple synthesis process, high energy density and desirable safetyperformance LiNi_(x)Co_(y)M_(1-x-y)O₂ is considered as one of the latestpositive active materials which may substitute LiCoO₂, and may be widelyused as positive active materials in hybrid vehicle batteries. However,some problems still exist for LiNi_(x)Co_(y)M_(1-x-y)O₂ as cathodematerial for secondary lithium battery, such as cell swelling at highcut-off voltage, particle pulverizing cycled hundred or thousand times,which may lead to safety accidents of secondary lithium battery due toovercharge or thermal runaway.

In order to improve the performances of LiNi_(x)Co_(y)M_(1-x-y)O₂, it isproposed that composite including lithium metal phosphate (LiMPO₄) andmetal phosphate (M₃(PO4)₂) can be coated on the surface of nickel-basedoxide positive active material, so as to improve the safety performanceof the secondary lithium battery via improving the thermal stability ofthe positive active material. However, the proposal mentioned abovestill has the following disadvantages. Firstly, M₃(PO₄)₂ can hardlytransmit into LiMPO₄; Secondly, it is difficult to control the ratio ofM₃(PO₄)₂ to LiMPO₄; Thirdly, the content of lithium on the surface ofnickel-based oxide positive active material has to be higher than thatin the core, which will limit the application of the positive activematerial; Fourthly, the coating layer is formed via sintering thecomposite deposited on the surface of the core. It is difficult to formcomplete and compact coating layer. Electrolyte and HF in theelectrolyte may contact the core that fails to be coated by the coatinglayer and react with the core. In addition, the coating layer isphysically bonded to the core. Therefore, after long time cycles, thecoating layer may peel off from the core and cannot protect the coreanymore.

In addition, it has been reported that oxides, such as Al₂O₃, AlPO₄,ZrO₂, TiO₂ and B₂O₃, can be used to coat the positive active materials,so as to improve the surface structural stability of the positive activematerials and improve the cycling performance of the lithium ionbatteries at high voltage. However, the metal oxides mentioned above forcoating the core are all non-electrochemically active materials havingpoor lithium ion conductivity. Therefore, the coating layer of metaloxides can hardly improve the performances of the positive activematerials. Some even may adversely affect the performances of thepositive active materials.

What is needed, therefore, is to provide a positive active materialhaving desirable performances for use in secondary lithium batteries andmethod for preparing the same.

BRIEF SUMMARY

One object of the present invention is to provide a positive activematerial having high capacity and stability as well as desirable safetyperformance and cycling performance for use in a secondary lithiumbattery and method for preparing the same. The other object of thepresent invention is to provide a secondary lithium battery which hashigh capacity and stability as well as desirable safety performance andcycling performance.

According to one embodiment of the present invention, a positive activematerial for use in a secondary lithium battery includes a core oflithium transition metal oxide represented by FormulaLi_(x)M_(y)N_(1-y)O_(2-α)A_(β) and a coating layer of lithium transitionmetal silicate represented by Formula x′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ)in-situ formed on the core, wherein the element represented by M is atleast one of Ni, Co and Mn; the element represented by N and N′ each isat least one of Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Ra, Al, Ga, In, Ge,Sn, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Ru, Rh, Pd,Ag, Cd, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; theelement represented by A and B each is at least one of N, F, P, S, Cl,Se; and 0.8≤x≤1.3, 0.6≤y≤1.0, 0.01≤x′≤2.1, 0.2≤y′≤1.5, 0.1≤a≤3.0,0≤α≤0.2, 0≤β≤0.4, 0≤λ<0.5, 0≤ζ≤0.5.

The coating layer of lithium transition metal silicate represented byFormula x′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) has desirable lithium ionconductivity and structural stability. The coating layer of lithiumtransition metal silicate represented by Formulax′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) at least has the following functions.

1) inhibiting oxygen evolution and structure change of the corerepresented by Formula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β) at high voltage:for the core without coating layer formed thereon, when the secondarylithium battery is charged to over 4.30 V, after deintercalation oflithium ions, the element represented by M mainly exists in +4. M⁴⁺ onthe surface of the core will change to M³⁺ or M²⁺, which will lead tostructure change of the core and oxygen evolution. Because the coatinglayer is in situ formed on the surface of the core via chemicalreaction, the coating layer can be bonded to the surface of the core viastable chemical bonding. Due to the protection of the coating layer, athigh voltage, oxygen evolution and change of M⁴⁺ into M³⁺ or M²⁺ isinhibited. Therefore, structural stability and cycling performance ofthe positive active material is remarkably improved.

2) preventing the secondary lithium battery from swelling via inhibitingthe core of lithium transition metal oxide from catalyzing and oxidizingthe electrolyte: the transition metal M in the core without lithiuminsertion mainly exist in +4 has strong catalyzing and oxidizingability, which may lead to decomposition of the electrolyte andgeneration of gas and further lead to swelling of the secondary lithiumbattery. After coating of the coating layer, polyanionic compound ofsilicate on the surface of the core will reduce the catalyzing andoxidizing ability of the core, and reduce the decomposition of theelectrolyte.

3) preventing HF in the electrolyte from corroding the core of lithiumtransition metal oxide: lithium transition metal oxide can be readilycorroded by HF in the electrolyte, while silicate can absorb F ion. Thecoating layer can prevent HF from directly contacting the core, whichwill reduce dissolution of transition metals from the core and improvethe stability of the positive active material.

Compared with the prior art, the coating layer of the positive activematerial for use in a secondary lithium battery according to the presentinvention can be stably bonded to the core and the coating layer hasdesirable lithium ion conductivity and structural stability. Thepositive active material according to the present invention has highcapacity, desirable cycling performance, desirable safety performance,and high thermal stability. The positive active material according tothe present invention also has a wider operating voltage range (having avoltage upper limit of 4.1 V-4.7 V) and stable thermal stability. Thesecondary lithium battery containing the positive active materialaccording to the present invention has high volumetric energy densityand desirable cycling performance

According to one aspect of the present invention, the elementrepresented by N′ and the element represented by N are same ordifferent, and the element represented by B and the element representedby A are same or different.

According to one aspect of the present invention, in the lithiumtransition metal oxide represented by FormulaLi_(x)M_(y)N_(1-y)O_(2-α)A_(β), the element represented by M iscombination of three elements of Ni, Co, Mn; the element represented byN is one or more of Mg, Al, Ti, B, V, Mo, W, Ni, Co, Mn, Y, Ce. Theelement represented by N can easily enter the crystal structure of thelithium transition metal oxide and improve the structural stabilitythereof.

According to one aspect of the present invention, the elementrepresented by M in the lithium transition metal oxide represented byFormula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β) is combination ofNi_(1/3)Co_(1/3)Mn_(1/3), Ni_(0.5)Co_(0.2)Mn_(0.3),Ni_(0.6)Co_(0.2)Mn_(0.2) and Ni_(0.8)Co_(0.1)Mn_(0.1). The combinationof Ni_(1/3)Co_(1/3)Mn_(1/3), Ni_(0.5)Co_(0.2)Mn_(0.3),Ni_(0.6)C_(0.2)Mn_(0.2) and Ni_(0.8)Co_(0.1)Mn_(0.1) has high structuresymmetry. The lithium transition metal oxide containing the combinationas previously described has desirable cycling performance.

According to one aspect of the present invention, in the lithiumtransition metal oxide represented by FormulaLi_(x)M_(y)N_(1-y)O_(2-α)A_(β), the element represented by M is Niand/or Co, the element represented by N is one or more of Mg, Al, Ti, B,V, Mo, W, Ni, Co, Mn, Y, Ce, 0.7≤y≤1.0. In this case, the elementrepresented by N can improve structural stability of the positive activematerial during delithiation and insertion of lithium ions.

According to one aspect of the present invention, the elementrepresented by M in the lithium transition metal oxide represented byFormula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β) is selected from a groupconsisting of Co, Ni_(0.5)Co_(0.5), Ni_(0.7)C^(0.3), Ni_(0.8)Co_(0.2),Ni_(0.8)Co_(0.1). In this case, the lithium transition metal oxide hasdesirable cycling performance.

According to one aspect of the present invention, the elementrepresented by N in the lithium transition metal oxide represented byFormula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β) is one or more of Mg, Al, Ti, Mo,Zr, B, V, Ce, W, 0.95≤y≤1.0. In this case, the positive active materialcan be readily to be synthesized.

According to one aspect of the present invention, the elementrepresented by N in the lithium transition metal oxide represented byFormula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β) is one or more of Mg, Al, Ti, Mo,Zr, B, V, Ce, W, 0.99≤y≤1.0. In this case, the positive active materialhas high specific capacity due to the reduction of element withoutelectrovalence change in the core.

According to one aspect of the present invention, the elementrepresented by A in the lithium transition metal oxide represented byFormula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β) is N or F, 0≤β≤0.1. In this case,the positive active material has desirable thermal stability and thesecondary lithium battery has desirable safety performance.

According to one aspect of the present invention, the elementrepresented by N′ in the lithium transition metal silicate representedby Formula x′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) is one or more of the elementrepresented by M and/or N in the lithium transition metal oxiderepresented by Formula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β).

According to one aspect of the present invention, the elementrepresented by B in the lithium transition metal silicate represented byFormula x′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) is N, F, 0≤ζ≤0.2.

According to one aspect of the present invention, in the lithiumtransition metal silicate represented by Formulax′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ), 0.1≤x′≤1, 0.2≤y′≤1.0.

According to one aspect of the present invention, in the lithiumtransition metal silicate represented by Formulax′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ), a=1.0, x′=1, y′=1. The coating layer ofLi₂O.N′O.SiO_(2-λ)B_(ζ) has desirable ion conductivity.

According to one aspect of the present invention, in the lithiumtransition metal silicate represented by Formulax′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ), a=1.5, x′=0.5, y′=1. In this case, thecoating layer of 0.5Li₂O.N′O_(1.5).SiO_(2-λ)B_(ζ) has desirable ionconductivity.

According to one aspect of the present invention, in the lithiumtransition metal silicate represented by Formulax′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ), a=2, x′=1, y′=1. The coating layer ofLi₂O.N′O₂.SiO_(2-λ)B_(ζ) has desirable ion conductivity and structuralstability.

According to one aspect of the present invention, the lithium transitionmetal silicate represented by Formula x′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) isa mixture of Li₂O.N′O.SiO_(2-λ)B_(ζ),0.5Li₂O.N′O_(1.5).SiO_(2-λ)B_(ζ)and Li₂O.N′O₂.SiO_(2-λ)B_(ζ).

According to one aspect of the present invention, the thickness of thelithium transition metal silicate represented by Formula x′Li₂Oy′N′O_(a).SiO_(2-λ)B_(ζ) is 0.1 nm˜500 nm, or preferably 1 nm˜300 nm Thecoating layer can conduct lithium ions and can hardly conductelectronics. If the thickness of the coating layer is more than 500 nm,the positive active material has poor electrochemical activity due toincrease of conductivity of the material. If the thickness of thecoating layer is less than 0.1 nm, the coating layer cannot coat thecore.

According to one aspect of the present invention, a mass content of thelithium transition metal silicate represented by Formulax′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) in the total positive active material isabout 0.01%˜30%, and preferably 0.1%˜5.0%.

According to one aspect of the present invention, a method for preparinga positive active material is provided. The method includes the stepsof: preparing the core of lithium transition metal oxide represented byFormula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β), adding Si source; and obtainingthe positive active material comprising the core of lithium transitionmetal oxide represented by Formula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β) andthe coating layer of the lithium transition metal silicate representedby Formula x′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) in-situ formed on the corevia sintering.

According to one aspect of the present invention, the Si source of thelithium transition metal silicate represented by Formula x′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) is one or more of elementary substance Si,SiO₂, SiO, H₄SiO₄, H₂SiO₃, Li₄SiO₄, Li₂SiO₃, LiHSiO₃, silicate ester,sub acid ester and a compound containing Si and at least two elementsselected from a group consisting of Li, C, H, O, N.

According to one aspect of the present invention, the method forpreparing a positive active material includes the steps of:

1) preparing the core of lithium transition metal oxide represented byFormula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β): preparing intermediates ofoxide, hydroxide and carbonate via one of solid milling method, liquidcoprecipitation method, sol-gel method, combustion method, solvothermalmethod, Pechini method; mixing the intermediates of oxide, hydroxide orcarbonate of transition metal with lithium source and materialcontaining element represented by A, or only adding lithium source; andsintering the mixture at 600˜1200° C. or preferably at 700-900° C.; or,obtaining mixture containing lithium and transition metal via one ofsolid milling method, liquid coprecipitation method, sol-gel method,combustion method, solvothermal method, Pechini method; and sinteringthe mixture at 600˜1200° C. or preferably at 700-900° C.;

2) adding a material containing Si source and element represented by Binto the core of lithium transition metal oxide represented by FormulaLi_(x)M_(y)N_(1-y)O_(2-α)A_(β) or only adding a material containing Sisource into the core of lithium transition metal oxide represented byFormula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β): uniformly dispersing thematerial containing Si source or containing Si source and elementrepresented by B in the core represented by FormulaLi_(x)M_(y)N_(1-y)O_(2-α)A_(β) via one of solid milling method, sol-gelmethod, liquid phase mixing method, vapor deposition method; and

3) solid phase sintering the mixture in step 2) at 400˜1200° C., orpreferably at 500˜900° C., and obtaining the positive active materialcomprising the core of lithium transition metal oxide represented byFormula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β) and the coating layer of lithiumtransition metal silicate represented by Formulax′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) in situ formed on the core.

Compared with the prior art, according to one embodiment of the presentinvention, the method for preparing positive active material can in situform coating layer of lithium transition metal silicate represented byFormula x′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) on the core of lithiumtransition metal oxide represented by FormulaLi_(x)M_(y)N_(1-y)O_(2-α)A_(β). The coating layer can be uniformlyformed on the surface of the core. Compared with prior art coatingmethod, the coating content of the coating layer of the positive activematerial according to the present invention can be controlled precisely.In addition, the method of the present invention is readily to berealized, readily to be carried out in industrial production, andmaintain the properties of the lithium transition metal oxides. Thepositive active material prepared according to the method of the presentinvention has high capacity, desirable cycling performance and desirablesafety performance.

According to one embodiment of the present invention, a secondarylithium battery is provided. The secondary lithium battery includes apositive electrode, a negative electrode and a separator between thepositive electrode and the negative electrode, wherein the positiveelectrode includes the positive active material as previously described.

According to one aspect of the present invention, the cut-off voltage ofthe secondary lithium battery is 4.1-4.7V.

Examples of the present invention will now be described more fullyhereinafter, in which some, but not all examples of the invention areshown. Indeed, the invention may be embodied in many different forms andshould not be construed as limited to the examples as set forth herein;rather, these examples are provided so that this disclosure will satisfyapplicable legal requirements.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS EXAMPLE 1

The positive active material of Example 1 includes a core ofLi_(1.07)Ni_(0.1)Co_(0.5)Mn_(0.4)O₂ obtained via coprecipitation methodand 0.5 wt % of coating layer of0.5Li₂O.0.1NiO.0.5CoO_(3/2).0.3MnO_(3/2).0.1MnO₂.SiO₂ having a thicknessof 100-200 nm.

The method for preparing the positive active material of Example 1includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 0.1:0.5:0.4 indeionized water and obtaining a mixed solution of 1 mol/L; adding 1mol/L NaOH solution in the mixed solution, fully stirring the mixedsolution and maintaining the temperature at 75° C., and obtaining loosecoprecipitate after full reaction; repeatedly washing the coprecipitatewith deionized water and ethanol; sintering the washed coprecipitate inair at 500° C. for 5 hours; fully mixing the sintered coprecipitate withLiOH.H₂O and sintering the mixture of coprecipitate and LiOH.H₂O in airat 900° C. for 10 hours, and obtaining the core ofLi_(1.07)Ni_(0.1)Co_(0.5)Mn_(0.4)O₂.

Mixing nano SiO₂ with the core of Li_(1.07)Ni_(0.1)Co_(0.5)Mn_(0.4)O₂ ata mass ratio of 0.0025:1; milling the mixture of nano SiO₂ and the coreof Li_(1.07)Ni_(0.1)Co_(0.5)Mn_(0.4)O₂ in a planetary ball mill having arotation speed of 300 r/min for 5 hours; sintering the fully milledmixture of nano SiO₂ and the core of Li_(1.07)Ni_(0.1)Co_(0.5)Mn_(0.4)O₂in air at 750° C. for 10 hours and obtaining a positive active materialincluding a core of Li_(1.07)Ni_(0.1)Co_(0.5)Mn_(0.4)O₂ and a coatinglayer of 0.5Li₂O.0.1NiO.0.5CoO_(3/2).0.3MnO_(3/2).0.1MnO₂.SiO₂.

EXAMPLE 2

The positive active material of Example 2 includes a core ofLi_(1.10)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂ obtained via coprecipitation methodand 0.01 wt % of coating layer of0.55Li₂O.1/3NiO.1/3CoO_(3/2).1/3MnO₂.SiO₂ having a thickness of 100-500nm coated on the core.

The method for preparing the positive active material of Example 2includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 1.0:1.0:1.0 indeionized water and obtaining a mixed solution of 1 mol/L; adding 1mol/L NaOH solution into the mixed solution, fully stirring the mixedsolution and maintaining the temperature at 75° C., and obtaining loosecoprecipitate after full reaction; repeatedly washing the coprecipitatewith deionized water and ethanol; sintering the washed coprecipitate inair at 500° C. for 5 hours; fully mixing the sintered coprecipitate withLiOH.H₂O and sintering the mixture of coprecipitate and LiOH.H₂O in airat 900° C. for 20 hours, and obtaining the core ofLi_(1.10)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂.

Mixing Li₂SiO₃ and the core of Li_(1.10)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂ at amass ratio of 0.0001:1; milling the mixture of Li₂SiO₃ and the core ofLi_(1.10)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂ in a planetary ball mill having arotation speed of 300 r/min for 5 hours; sintering the fully milledmixture of Li₂SiO₃ and the core of Li_(1.10)N_(1/3)Co_(1/3)Mn_(1/3)O₂ inair at 550° C. for 10 hours and obtaining a positive active materialincluding the core of Li_(1.10)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂ and thecoating layer of 0.55Li₂O.1/3NiO.1/3CoO_(3/2).1/3MnO₂.SiO₂.

EXAMPLE 3

The positive active material of Example 3 includes a core ofLi_(1.05)Ni_(0.5)Co_(0.2)Mn_(0.3)O₂ obtained via combustion method and30.0 wt % of coating layer of0.54Li₂O.0.3NiO.0.2NiO_(3/2).0.2CoO_(3/2).0.3MnO₂.SiO₂ having athickness of 50-80 nm coated on the core.

The method for preparing the positive active material of Example 3includes the steps of:

Dissolving lithium nitrate, nickel nitrate, cobalt nitrate, manganesenitrate at an atom ratio of 1.07:0.50:0.20:0.30 in ethanol in acontainer and obtaining a mixed solution; adding glycerol into the mixedsolution after lithium nitrate, nickel nitrate, cobalt nitrate andmanganese nitrate being fully dissolved, the ratio of glycerol to thetotal metal ions is 3:1; stirring the mixed solution in the contained ina water bath at 80° C. to evaporate the ethanol; moving the container toa resistance furnace and heating after the ethanol being fullyevaporated, until the residue of the mixed solution fully combusting;collecting the combustion product and sintering the combustion productsin air at 750° C. for 5 hours and obtaining the core ofLi_(1.05)Ni_(0.5)CO_(0.2)Mn_(0.3)O₂;

Dissolving H₄SiO₄ and Li_(1.05)Ni_(0.5)Co_(0.2)Mn_(0.3)O₂ at a massratio of 0.19:1 in 500 mL deionized water in a container and obtaining amixed solution; after H₄SiO₄ and Li_(1.05)Ni_(0.5)Co_(0.2)Mn_(0.3)O₂being fully dissolved, moving the container having the mixed solution toa water bath at 80° C. and stirring to evaporate the water; moving thecontainer into an oven at 160° C. for 5 hours and obtaining blackpowder; sintering the black powder in air at 650° C. for 10 hours, andobtaining a positive active material including the core ofLi_(1.05)Ni_(0.5)Co_(0.2)Mn_(0.3)O₂ and the coating layer of0.54Li₂O.0.3NiO.0.2NiO_(3/2).0.2CoO_(3/2).0.3MnO₂.SiO₂.

EXAMPLE 4

The positive active material of Example 4 includes a core ofLi_(1.20)Ni_(0.5)Co_(0.2)Mn_(0.29)Zr_(0.01)O_(1.98)F_(0.04) obtained viasol gel method and 3.0 wt % of coating layer of0.53Li₂O.0.3NiO.0.2NiO_(3/2).0.2CoO_(3/2).0.3MnO₂.0.01ZrO₂.SiO_(1.98)F_(0.04)having a thickness of 100-200 nm coated on the core.

The method for preparing the positive active material of Example 4includes the steps of:

Dissolving lithium acetate, nickel acetate, cobalt acetate, manganeseacetate, nano titanium dioxide, ammonium fluoride at an atom ratio of1.23:0.50:0.20:0.29:0.01:0.04 in deionized water in a container andobtaining a mixed solution; adding citric acid into the mixed solutionafter lithium acetate, nickel acetate, cobalt acetate, manganeseacetate, nano-titanium dioxide, ammonium fluoride being fully dissolved,the ratio of citric acid to the total metal ions is 2:1; stirring themixed solution in the container in a water bath at 85° C. to evaporatethe water and obtaining gelatinous substance; moving the container to anoven at a 160° C. and heating for 5 hours, and obtaining brown-blacksubstance; milling the brown-black substance into powder, sintering thepowder in air at 750° C. for 25 hours and obtaining the core ofLi_(1.20)Ni_(0.5)Co_(0.2)Mn_(0.29)Zr_(0.01)O_(1.98)F_(0.04);

Dissolving orthosilicate ester andLi_(1.20)Ni_(0.5)Co_(0.2)Mn_(0.29)Zr_(0.01)O_(1.98)F_(0.04) at a massratio of 0.0268:1 in 500 mL alcohol in a container and obtaining a mixedsolution; setting the container having the mixed solution in a waterbath at 70° C. and stirring to evaporate the alcohol and theorthosilicate ester; placing the container in an oven at 160° C. for 5hours and obtaining black powder; sintering the black powder in air at850° C. for 10 hours, and obtaining a positive active material includingthe core of Li_(1.20)Ni_(0.5)Co_(0.2)Mn_(0.29)Zr_(0.01)O_(1.98)F_(0.04)and a coating layer of0.53Li₂O.0.3NiO.0.2NiO_(3/2).0.2CoO_(3/2).0.3MnO₂.0.01ZrO₂.SiO_(1.98)F_(0.04).

EXAMPLE 5

The positive active material of Example 5 includes a core ofLi_(0.98)Ni_(0.6)Co_(0.18)Mn_(0.2)Ti_(0.02)O₂ obtained viacoprecipitation method and 0.40 wt % of coating layer of0.49Li₂O.0.2NiO.0.4Ni_(3/2).0.18CoO_(3/2).0.2MnO_(0.2).0.02TiO₂.SiO₂having a thickness of 10-15 nm.

The method for preparing the positive active material of Example 5includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄, nano TiO₂ at an atom ratio of0.60:0.18:0.20:0.02 in deionized water and obtaining a mixed solution of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution, fullystirring the mixed solution and maintaining the temperature at 75° C.,and obtaining loose coprecipitate after full reaction; washing thecoprecipitate with deionized water and ethanol repeatedly; sintering thewashed coprecipitate in air at 500° C. for 5 hours; fully mixing thesintered coprecipitate with Li₂CO₃ and sintering the mixture of thesintered coprecipitate and Li₂CO₃ in air at 750° C. for 10 hours, andobtaining a core of Li_(0.98)Ni_(0.6)Co_(0.18)Mn_(0.2)Mn_(0.02)O₂.

Mixing SiO₂ with the core ofLi_(0.98)Ni_(0.6)Co_(0.18)Mn_(0.2)Ti_(0.02)O₂ at a mass ratio of0.002:1; milling the mixture of SiO₂ and the core ofLi_(0.98)Ni_(0.6)Co_(0.18)Mn_(0.2)Ti_(0.02)O₂ in a planetary ball millhaving a rotation speed of 500 r/min for 5 hours; sintering the fullymilled mixture in air at 900° C. for 2 hours and obtaining a positiveactive material including the core ofLi_(0.98)Ni_(0.6)Co_(0.18)Mn_(0.2)Ti_(0.02)O₂ and the coating layer of0.49Li₂O.0.2NiO.0.4NiO_(3/2).0.18CoO_(3/2).0.2MnO₂.0.02TiO₂.SiO₂.

EXAMPLE 6

The positive active material of Example 6 includes a core ofLi_(0.92)Ni_(0.75)Co_(0.15)Mn_(0.1)O₂ obtained via Pechini method and0.35 wt % of coating layer of0.45Li₂O.0.1NiO.0.65NiO_(3/2).0.15CoO_(3/2).0.1MnO₂.SiO₂ having athickness of 15-20 nm.

The method for preparing the positive active material of Example 6includes the steps of:

Dissolving LiNO₃, NiNO₃, CoNO₃, MnNO₃ at an atom ratio of0.94:0.75:0.15:0.10 in deionized water in a container and obtaining ametal ion solution having a metal ion concentration of 1 mol/L;dissolving citric acid in polyethylene glycol and obtaining a citricacid solution of 1.5 mol/L; mixing the metal ion solution and the citricacid solution at a ratio of 2:1, and heating the container having themixture of the metal ion solution and the citric acid solution in an oilbath at 130° C. until the mixture in the container turning into blacksticky substance; moving the container into a Muffle furnace andprefiring at 300° C. for 5 hours; milling the prefired product intopowder, sintering the powder in air at 800° C. for 10 hours, andobtaining the core of Li_(0.92)Ni_(0.75)Co_(0.15)Mn_(0.1)O₂

Mixing SiO₂ with the core of Li_(0.92)Ni_(0.75)Co_(0.15)Mn_(0.1)O₂ at amass ratio of 0.0023:1; milling the mixture of SiO₂ and the core ofLi_(0.92)Ni_(0.75)Co_(0.15)Mn_(0.1)O₂ in a planetary ball mill having arotation speed of 500 r/min for 5 hours; sintering the fully milledmixture in air at 600° C. for 2 hours and obtaining a positive activematerial including the core of Li_(0.92)Ni_(0.75)Co_(0.15)Mn_(0.1)O₂ andthe coating layer of0.45Li₂O.0.1NiO0.65NiO_(3/2).0.15CoO_(3/2).0.1MnO₂.SiO₂.

EXAMPLE 7

The positive active material of Example 7 includes a core ofLi_(1.02)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂ obtained via coprecipitation methodand 0.50 wt % of coating layer of0.51Li₂O.0.09NiO.0.63NiO_(3/2).0.09CoO_(3/2).0.09MnO₂.0.1V₂O₅.SiO₂having a thickness of 40-50 nm.

The method for preparing the positive active material of Example 7includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 0.80:0.10:0.10 indeionized water and obtaining a mixed solution of 1 mol/L; adding 1mol/L NaOH solution into the mixed solution, stirring the mixed solutionand maintaining the temperature at 75° C., and obtaining loosecoprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; sintering the washedcoprecipitate in air at 500° C. for 5 hours; fully mixing the sinteredcoprecipitate with LiOH.H₂O and sintering the mixture of thecoprecipitate and LiOH.H₂O in air at 900° C. for 20 hours, and obtainingthe core of Li_(1.02)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂.

Milling SiO₂, NH₄VO₃ and the core of Li_(1.02)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂at a mass ratio of 0.0045:0.0004:1 in a planetary ball mill having arotation speed of 300 r/min for 5 hours; sintering the fully milledmixture of SiO₂, NH₄VO₃ and the core ofLi_(1.02)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂ in air at 750° C. for 10 hours andobtaining a positive active material including the core ofLi_(1.02)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂ and the coating layer of0.51Li₂O.0.09NiO.0.63NiO_(3/2).0.09CoO_(3/2).0.09MnO₂.0.1V₂O₅.SiO₂.

EXAMPLE 8

The positive active material of Example 8 includes a core ofLi_(1.06)Ni_(0.82)Co_(0.10)Mn_(0.07)Zr_(0.004)Mg_(0.002)Ti_(0.004)O₂obtained via coprecipitation method and 0.25 wt % of coating layer of0.531Li₂O.0.07NiO.0.75NiO_(3/2).0.1CoO_(3/2).0.07MnO₂.0.004ZrO₂.0.002MgO₂.0.1TiO₂.SiO₂having a thickness of 12-15 nm.

The method for preparing the positive active material of Example 8includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 0.82:0.10:0.07 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, and maintaining the temperature at 75° C.; obtaining loosecoprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; mixing the washed redcoprecipitate with Li₂CO₃, nano ZrO₂, nano MgO, nanoTiO₂ in an inclinedmixer having a rotation speed of 50 r/min for 5 hours; sintering themixture of the washed coprecipitate, Li₂CO₃, nano ZrO₂, nano MgO andnanoTiO₂ in air at 800° C. for 5 hours, and obtaining the core ofLi_(1.07)Ni_(0.82)Co_(0.10)Mn_(0.07)Zr_(0.004)Mg_(0.002)Ti_(0.004)O₂.

Dissolving methyl silicate andLi_(1.07)Ni_(0.82)Co_(0.10)Mn_(0.07)Zr_(0.004)Mg_(0.002)Ti_(0.004)O₂ ata mass ratio of 0.0035:1 in 500 mL alcohol in a container and obtaininga mixed solution after fully dissolution; adding 1 mol citric acid intothe mixed solution after full dissolution of the methyl silicate,setting the container having the mixed solution in a water bath at 70°C. and stirring to evaporate the alcohol; placing the container in anoven at 160° C. for 5 hours and obtaining black powder; sintering theblack powder in air at 650° C. for 5 hours, and obtaining a positiveactive material including the core ofLi_(1.07)Ni_(0.82)Co_(0.10)Mn_(0.07)Zr_(0.004)Mg_(0.002)Ti_(0.004)O₂ andthe coating layer of0.531Li₂O.0.07NiO.0.75NiO_(3/2).0.1CoO_(3/2).0.07MnO₂.0.004ZrO₂.0.002MgO₂.0.1TiO₂.SiO₂.

EXAMPLE 9

The positive active material of Example 9 includes a core ofLi_(0.97)Ni_(0.9)Co_(0.05)Mn_(0.04)Mg_(0.01)O₂ obtained viacoprecipitation method and 0.15 wt % of coating layer of0.5Li₂O.0.04NiO.0.86NiO_(3/2).0.05CoO_(3/2).0.04MnO₂.0.01MgO.SiO₂ havinga thickness of 8-10 nm.

The method for preparing the positive active material of Example 9includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 0.9:0.05:0.04 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, while maintaining the temperature at 70° C.; obtaining loosecoprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; mixing the coprecipitate withnano MgO in an inclined mixer having a rotation speed of 50 r/min for 5hours; mixing the mixture of the coprecipitate and nano MgO withLiOH.H₂O, sintering the mixture in air at 800° C. for 10 hours, andobtaining the core of Li_(0.97)Ni_(0.9)Co_(0.05)Mn_(0.04)Mg_(0.01)O₂.

Mixing H₄SiO₄ with the core ofLi_(0.97)Ni_(0.9)Co_(0.05)Mn_(0.04)Mg_(0.01)O₂ at a mass ratio of0.0011:1; milling the mixture of the core ofLi_(0.97)Ni_(0.9)Co_(0.05)Mn_(0.04)Mg_(0.01)O₂ and H₄SiO₄ in a planetaryball mill having a rotation speed of 500 r/min for 5 hours; sinteringthe milled mixture of H₄SiO₄ and the core ofLi_(0.97)Ni_(0.9)Co_(0.05)Mn_(0.04)Mg_(0.01)O₂ in air at 600° C. for 2hours and obtaining a positive active material including the core ofLi_(0.97)Ni_(0.9)Co_(0.05)Mn_(0.04)Mg_(0.01)O₂ and the coating layer of0.5Li₂O.0.04NiO.0.86NiO_(3/2).0.05CoO_(3/2).0.04MnO₂.0.01MgO.SiO₂.

EXAMPLE 10

The positive active material of Example 10 includes a core ofLi_(1.08)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂ obtained via solid milling methodand 17.0 wt % of coating layer of0.54Li₂O.1/3NiO.1/3CoO_(3/2).1/3MnO₂.SiO₂ having a thickness of 20-50nm.

The method for preparing the positive active material of Example 10includes the steps of:

Mixing Li₂CO₃, nickel oxalate, cobalt oxalate, MnCO₃ at a molar ratio of0.56:1.0:1.0:1.0 in a zirconia sander having a rotation speed of 1000r/min for 5 hours, the diameter of the zirconia milling media is 3 mm,and the ratio of zirconia milling media to the mixture of Li₂CO₃, nickeloxalate, cobalt oxalate and MnCO₃ is 1:1; removing the zirconia millingmedia and sintering the remained mixture in air at 750° C. for 5 hoursand obtaining the core of Li_(1.08)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂.

Dissolving TEOS and the core of Li_(1.08)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂ at amass ratio of 0.1030:1 in 500 mL alcohol in a container and obtaining amixed solution after TEOS and the core ofLi_(1.08)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂ being fully hydrolyzed; setting thecontainer having the mixed solution in a water bath at 70° C. andstirring so as to evaporate the alcohol; placing the container in anoven at 180° C. for 5 hours and obtaining black powder; sintering theblack powder in air at 850° C. for 6 hours, and obtaining a positiveactive material including the core ofLi_(1.08)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂ and the coating layer of0.54Li₂O.1/3NiO.1/3CoO_(3/2).1/3MnO₂.SiO₂.

EXAMPLE 11

The positive active material of Example 11 includes a core ofLi_(1.04)Ni_(0.5)CO_(0.2)Mn_(0.28)Zr_(0.02)O_(1.98)F_(0.04) obtained viacoprecipitation and solid milling method and 2.0 wt % of a coating layerof0.52Li₂O.0.28NiO.0.22NiO_(3/2).0.2CoO_(3/2).0.28MnO₂.0.02ZrO₂.SiO_(1.98)F_(0.04)having a thickness of 180-200 nm.

The method for preparing the positive active material of Example 11includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 0.50:0.20:0.28 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, while maintaining the temperature at 70° C.; obtaining loosecoprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; mixing the washed coprecipitatewith LiOH.H₂O, nano ZrO₂ and NH₄F in a zirconia sander having a rotationspeed of 800 r/min and mixing for 5 hours, the diameter of the zirconiamilling media is 3 mm, and the ratio of the zirconia milling media tothe mixture of the washed coprecipitate and LiOH.H₂O, nano ZrO₂, NH₄F is1:1; removing the zirconia milling media and sintering the remainedmixture in air at 950° C. for 24 hours and obtaining the core ofLi_(1.04)Ni_(0.5)Co_(0.2)Mn_(0.28)Zr_(0.02)O_(1.98)F_(0.04).

Mixing nano SiO₂ with the core ofLi_(1.04)Ni_(0.5)Co_(0.2)Mn_(0.28)Zr_(0.02)O_(1.98)F_(0.04) at a massratio of 0.0200:1; milling the mixture of SiO₂ and the core ofLi_(1.04)Ni_(0.5)Co_(0.2)Mn_(0.28)Zr_(0.02)O_(1.98)F_(0.04) in aninclined mixer having a rotation speed of 50r/min for 10 hours;sintering the fully milled mixture in air at 750° C. for 6 hours andobtaining a positive active material including the core ofLi_(1.04)Ni_(0.5)Co_(0.2)Mn_(0.28)Zr_(0.02)O_(1.98)F_(0.04) and thecoating layer of0.52Li₂O.0.28NiO.0.22NiO_(3/2).0.2CoO_(3/2).0.28MnO₂.0.02ZrO₂.SiO_(1.98)F_(0.04).

EXAMPLE 12

The positive active material of Example 12 includes a core ofLi_(1.05)Ni_(0.5)Co_(0.2)Mn_(0.28)Zr_(0.02)O_(1.98)F_(0.04) obtained viasol-gel method and 2.0 wt % coating layer of0.53Li₂O.0.28NiO.0.22NiO_(3/2).0.2CoO_(3/2).0.28MnO₂.0.02ZrO₂.SiO_(1.98)N_(0.01)having a thickness of 8-10 nm.

The method for preparing the positive active material of Example 12includes the steps of:

Dissolving lithium acetate, nickel acetate, cobalt acetate, manganeseacetate, nano titanium dioxide, ammonium fluoride at an atom ratio of1.07:0.50:0.20:0.28:0.02:0.04 in deionized water in a container andobtaining a mixed solution; adding citric acid into the mixed solutionafter lithium acetate, nickel acetate, cobalt acetate, manganeseacetate, nano titanium dioxide, ammonium fluoride being fully dissolved,the ratio of citric acid to the total metal ions is 2:1; stirring themixed solution in the container in a water bath at 85° C., to evaporatethe water and obtain gelatinous substance; placing the container in anoven at 160° C. for 5 hours, and obtaining brown-black substance;milling the brown-black substance in a zirconia sander having a rotationspeed of 800 r/min for 5 hours, the diameter of the zirconia millingmedia is 2 mm, and the ratio of the zirconia milling media to thebrown-black substance is 1:1; removing the zirconia milling media andsintering the remaining brown-black substance in air at 750° C. for 5hours and obtaining the core ofLi_(1.05)Ni_(0.5)Co_(0.2)Mn_(0.28)Zr_(0.02)O_(1.98)F_(0.04).

Dissolving TEOS and the core ofLi_(1.05)Ni_(0.5)Co_(0.2)Mn_(0.28)Zr_(0.02)O_(1.98)F_(0.04) at a massratio of 0.0480:1 in 500 mL glycol in a container and obtaining a mixedsolution; setting the container having the mixed solution in a 800 LPTFE sealing container and placing and sealing the container in astainless steel housing; placing the container in an oven at 175° C. for5 hours and obtaining black powder; sintering the black powder in amixed atmosphere of nitrogen and ammonia air at 550° C. for 10 hours,and obtaining a positive active material including the core ofLi_(1.05)Ni_(0.5)Co_(0.2)Mn_(0.28)Zr_(0.02)O_(1.98)F_(0.04) and thecoating layer of0.53Li₂O.0.28NiO.0.22NiO_(3/2).0.2CoO_(3/2).0.28MnO₂.0.02ZrO₂.SiO_(1.98)N_(0.01).

EXAMPLE 13

The positive active material of Example 13 includes a core ofLi_(1.05)Ni_(0.8)Co_(0.1)Mn_(0.1)O_(1.98)N_(0.01) obtained via solidmilling method and 7.0 wt % of coating layer of0.52Li₂O.0.1NiO.0.7NiO_(3/2).0.1CoO_(3/2).0.1MnO₂.SiO₂ having athickness of 20-30 nm.

The method for preparing the positive active material of Example 13includes the steps of:

Milling Li₂CO₃, nickel oxalate, cobalt oxalate, MnCO₃, urea at a molarratio of 0.53:0.8:0.1:0.1:0.15 in a zirconia sander having a rotationspeed of 1000 r/min for 5 hours, the diameter of the zirconia millingmedia is 5 mm, and the ratio of the zirconia milling media to themixture of Li₂CO₃, nickel oxalate, cobalt oxalate, MnCO₃, urea is 1:2;removing the zirconia milling media and sintering the remaining mixturein air at 750° C. for 5 hours and obtaining the core ofLi_(1.05)Ni_(0.8)Co_(0.1)Mn_(0.1)O_(1.98)N_(0.01).

Placing the core of Li_(1.05)Ni_(0.8)Co_(0.1)Mn_(0.1)O_(1.98)N_(0.01) ina tube furnace at 500° C.; adopting nitrogen having a flow rate of 1L/min as carrier gas; introducing a toluene solution having 0.2 mol/LTEOS into the tube furnace, to deposit TEOS on the surface of the coreof Li_(1.05)Ni_(0.8)Co_(0.1)Mn_(0.1)O_(1.98)N_(0.01); sintering the coreof Li_(1.05)Ni_(0.8)Co_(0.1)Mn_(0.1)O_(1.98)N_(0.01) having TEOSdeposited thereon in air at 700° C. for 5 hours, and obtaining apositive active material including the core ofLi_(1.05)Ni_(0.8)Co_(0.1)Mn_(0.1)O_(1.98)N_(0.01) and the coating layerof 0.52Li₂O.0.1NiO.0.7NiO_(3/2).0.1CoO_(3/2).0.1MnO₂.SiO₂.

EXAMPLE 14

The positive active material of Example 14 includes a core ofLi_(1.08)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂ obtained via coprecipitation methodand 0.10 wt % of coating layer of0.54Li₂O.1/3NiO.1/3CoO_(3/2).1/3MnO₂.SiO₂ having a thickness of 200-300nm.

The method for preparing the positive active material of Example 14includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 1.0:1.0:1.0 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, as well as maintaining the temperature at 75° C.; obtainingloose coprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; sintering the washedcoprecipitate in air at 500° C. for 5 hours and obtaining secondaryparticles of oxide or hydroxide A; milling nickel oxalate, cobaltoxalate, MnCO₃ at a molar ratio of 1.0:1.0:1.0 in a zirconia sanderhaving a rotation speed of 1000 r/min for 5 hours, the diameter of thezirconia milling media is 5 mm, and the ratio of zirconia milling mediato the mixture of nickel oxalate, cobalt oxalate, MnCO₃ is 1:1; removingthe zirconia milling media and sintering the remaining mixture in air at700° C. for 5 hours and obtaining oxide or hydroxide or carbonate B ofthe primary particles; mixing A and B, and mixing the mixture f A and Bwith LiOH.H₂O, sintering the mixture of A , B and LiOH.H₂O in air at800° C. for 5 hours, and obtaining the core ofLi_(1.08)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂.

Sintering the mixture of SiO₂ and the core ofLi_(1.08)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂ at a mass ratio of 0.0005:1 in airat 700° C. for 10 hours and obtaining a positive active materialincluding the core of Li_(1.08)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂ and a coatinglayer of 0.54Li₂O.1/3NiO.1/3CoO_(3/2).1/3MnO₂.SiO₂.

EXAMPLE 15

The positive active material of Example 15 includes a core ofLi_(1.03)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂ obtained via coprecipitation methodand 0.5 wt % of coating layer of0.52Li₂O.0.1NiO.0.7NiO_(3/2).0.1CoO_(3/2).0.1MnO₂.SiO₂ having athickness of 15-20 nm.

The method for preparing the positive active material of Example 15includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 0.80:0.10:0.10 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, as well as maintaining the temperature at 70° C.; obtainingloose coprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; fully mixing the washedcoprecipitate with LiOH.H₂O and sintering the mixture of thecoprecipitate and LiOH.H₂O in air at 850° C. for 10 hours, and obtainingthe core of Li_(1.03)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂.

Mixing and milling H₄SiO₄ with the core ofLi_(1.03)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂ at a mass ratio of 0.0034:1 in aninclined mixer having a rotation speed of 30 r/min for 10 hours;sintering the fully milled mixture in air at 850° C. for 6 hours andobtaining a positive active material including the core ofLi_(1.03)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂ and the coating layer of0.52Li₂O.0.1NiO..0.7NiO_(3/2).0.1CoO_(3/2).0.1MnO₂.SiO₂.

EXAMPLE 16

The positive active material of Example 16 includes a core ofLi_(1.04)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂obtained via coprecipitation methodand 0.7 wt % of coating layer of0.52Li₂O.0.1NiO.0.7NiO_(3/2).0.1CoO_(3/2).0.1MnO₂.SiO₂ having athickness of 15-20 nm.

The method for preparing the positive active material of Example 16includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 0.8:0.1:0.1 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, and maintaining the temperature at 70° C.; obtaining loosecoprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repatedly; sintering the washedcoprecipitate in air at 850° C. for 10 hours; fully mixing the sinteredcoprecipitate with LiOH.H₂O and sintering the mixture of thecoprecipitate and LiOH.H₂O in air at 850° C. for 10 hours, and obtainingthe core of Li_(1.04)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂.

Mixing and milling H₄SiO₄ with the core ofLi_(1.04)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂ at a mass ratio of 0.0060:1 in aplanetary ball mill having a rotation speed of 500 r/min for 5 hours;sintering the fully milled mixture in air at 500° C. for 2 hours andobtaining a positive active material including the core ofLi_(1.04)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂ and the coating layer of0.52Li₂O.0.1NiO.0.7NiO_(3/2).0.1CoO_(3/2).0.1MnO₂.SiO₂.

EXAMPLE 17

The positive active material of Example 17 includes a core ofLi_(1.05)CoO₂ obtained via coprecipitation method and 0.01 wt % of acoating layer of 0.53Li₂O.CoO_(3/2).SiO₂ having a thickness of 50˜100nm.

The method for preparing the positive active material of Example 17includes the steps of:

Preparing 1 mol/L CoSO₄ solution; slowly dripping 1 mol/L NH₄HCO₃solution at a dripping rate of 1 L/h into the CoSO₄ solution; aftercoprecipitation, filtering and washing the coprecipitate with deionizedwater, and obtaining CoCO₃ after drying; mixing Li₂CO₃ and CoCO₃ at amolar ratio of 1.07:1 in a planetary ball mill having a rotation speedof 200 r/min for 5 hours; sintering the fully mixed mixture of Li₂CO₃and CoCO₃ in air at 900° C. for 10 hours;

Adding H₄SiO₄ and the sintered product in a container having 500 mLalcohol; heating the container in a water bath at 75° C. and stirring toevaporate the alcohol; placing the container in an oven at 180° C. for 5hours, and obtaining black powder; sintering the black powder in air at650° C. for 6 hours, and obtaining a positive active material includingthe core of Li_(1.05)CoO₂and the coating layer of0.53Li₂O.CoO_(3/2).SiO₂.

EXAMPLE 18

The positive active material of Example 18 includes a core ofLi_(1.01)CoO_(0.89)Mg_(0.05)Al_(0.04)Ti_(0.02)O₂ obtained via sol-gelmethod and 0.4 wt % of coating layer of0.51Li₂O.0.89CoO_(3/2).0.05MgO.0.04AlO_(3/2).0.02TiO₂.SiO₂ having athickness of 15˜20 nm. The core ofLi_(1.01)Co_(0.89)Mg_(0.05)Al_(0.04)Ti_(0.02)O₂ is consisted ofmonocrystalline particles.

The method for preparing the positive active material of Example 18includes the steps of:

Dissolving lithium acetate, cobalt acetate, nano magnesia, nano aluminaand nano titanium dioxide at a metal atom ratio of1.03:0.89:0.05:0.04:0.02 in deionized water in a container and obtaininga mixed solution; adding citric acid into the mixed solution afterlithium acetate, cobalt acetate, nano magnesia, nano alumina and nanotitanium dioxide being fully dissolved, the ratio of citric acid to thetotal metal ions is 2:1; stirring the mixed solution in the container ina water bath at 85° C., to evaporate the water and obtain gelatinoussubstance; placing the container in an oven at 160° C. for 5 hours andobtaining brown-black substance; milling the brown-black substance intopowder, sintering the powder in air at 900° C. for 24 hours andobtaining the core of Li_(1.01)CoO_(0.89)Mg_(0.05)Al_(0.04)Ti_(0.02)O₂;

Dispersing the core of Li_(1.01)Co_(0.89)Mg_(0.05)Al_(0.04)Ti_(0.02)O₂in 0.2% H₄SiO₄ solution having a concentration of 500 g/L and obtaininga mixed solution; placing the mixed solution in water bath of 85° C., toevaporate the water and obtain gelatinous substance; sintering thegelatinous substance in air at 750° C. for 5 hours, and obtaining apositive active material including the core ofLi_(1.01)Co_(0.89)Mg_(0.05)Al_(0.04)Ti_(0.02)O₂ and the coating layer of0.51Li₂O.0.89CoO_(3/2)0.05MgO.0.04AlO_(3/2).0.02TiO₂.SiO₂.

EXAMPLE 19

The positive active material of Example 19 includes a core ofLi_(0.98)Co_(0.6)Al_(0.38)Ti_(0.02)O₂ obtained via coprecipitationmethod and 2.00 wt % of coating layer of0.49Li₂O.0.6CoO_(3/2).0.38AlO_(3/2).0.02TiO₂.SiO₂ having a thickness of100˜150 nm. The core of Li_(0.98)Co_(0.6)Al_(0.38)Ti_(0.02)O₂ isconsisted of monocrystalline particles.

The method for preparing the positive active material of Example 19includes the steps of:

Preparing 1 mol/L CoSO₄ solution; slowly dripping 1 mol/L NH₄HCO₃solution at a dripping rate of 1 L/h into the CoSO₄ solution; aftercoprecipitation, filtering and washing the coprecipitate with deionizedwater, obtaining CoCO₃ after drying; mixing Li₂CO₃, CoCO₃, nano Al₂O₃and nano TiO₂ at a molar ratio of 1.01:0.60:0.38:0.02 in a planetaryball mill having a rotation speed of 200 r/min for 5 hours; sinteringthe fully mixed mixture of Li₂CO₃, CoCO₃, nano Al₂O₃ and nano TiO₂ inair at 800° C. for 18 hours;

Mixing and milling SiO₂ with the sintered mixture above at a mass ratioof 0.01:1 in a planetary ball mill having a rotation speed of 300 r/minfor 5 hours; sintering the fully milled mixture in air at 750° C. for 10hours and obtaining a positive active material including the core ofLi_(0.98)Co_(0.6)Al_(0.8)Ti_(0.02)O₂ and the coating layer of0.49Li₂O.0.6CoO_(3/2).0.38AlO_(3/2)0.02TiO₂.SiO₂.

EXAMPLE 20

The positive active material of Example 20 includes a core ofLi_(1.02)Ni_(0.85)Co_(0.10)Al_(0.05)O₂ obtained via coprecipitationmethod and 0.45 wt % of coating layer of0.51Li₂O.0.85NiO_(3/2)0.1CoO_(3/2).0.05AlO_(3/2).SiO₂ having a thicknessof 15˜20 nm.

The method for preparing the positive active material of Example 20includes the steps of:

Dissolving NiSO₄, CoSO₄, Al(NO₃)₃ at an atom ratio of 0.85:0.10:0.05 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, and maintaining the temperature at 75° C. and dripping ammoniainto the mixed solution to maintain the pH value at 10.6; obtainingloose coprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; sintering the washedcoprecipitate in air at 500° C. for 5 hours; fully mixing the sinteredcoprecipitate with LiOH.H₂O and sintering the mixture of thecoprecipitate and LiOH.H₂O in air at 750° C. for 10 hours, and obtaininga core of Li_(1.02)Ni_(0.85)Co_(0.10)Al_(0.05)O₂.

Mixing and milling SiO₂ with the core ofLi_(1.02)Ni_(0.85)Co_(0.10)Al_(0.05)O₂ at a mass ratio of 0.0025:1 in aplanetary ball mill having a rotation speed of 300 r/min for 5 hours;sintering the fully milled mixture in air at 750° C. for 10 hours andobtaining a positive active material including the core ofLi_(1.02)Ni_(0.85)Co_(0.10)Al_(0.05)O₂ and the coating layer of0.51Li₂O.0.85NiO_(3/2)0.1CoO_(3/2).0.05AlO_(3/2).SiO₂.

EXAMPLE 21

The positive active material of Example 21 includes a core ofLi_(1.05)Ni_(0.90)Co_(0.08)Al_(0.02)O₂ obtained via sol-gel method and2.5 wt % of coating layer of0.53Li₂O.0.9NiO_(3/2)0.08CoO_(3/2).0.02AlO_(3/2).SiO₂ having a thicknessof 100˜150 nm.

The method for preparing the positive active material of Example 21includes the steps of:

Dissolving lithium acetate, nickel acetate, cobalt acetate, aluminumnitrate at an atom ratio of 1.09:0.90:0.08:0.02 in deionized water in acontainer and obtaining a mixed solution; adding citric acid into themixed solution after lithium acetate, nickel acetate, cobalt acetate,aluminum nitrate being fully dissolved, the ratio of citric acid to thetotal metal ions is 2:1; stirring the mixed solution in the container ina water bath at 85° C. to evaporate the water and obtain gelatinoussubstance; placing the container in an oven at 160° C. for 5 hours, andobtaining brown-black substance; milling the brown-black substance intopowder, sintering the powder in air at 750° C. for 5 hours and obtainingthe core of Li_(1.05)Ni_(0.90)Co_(0.08)Al_(0.02)O₂;

Dispersing the sintered core of Li_(1.05)Ni_(0.90)Co_(0.08)Al_(0.02)O₂in 0.8% orthosilicate solution at a concentration of 500 g/L andobtaining a mixed solution; setting the mixed solution in water bath of85° C. to evaporate the water and obtain gelatinous substance; sinteringthe gelatinous substance in air at 750° C. for 5 hours, and obtaining apositive active material including the core ofLi_(1.05)Ni_(0.90)Co_(0.08)Al_(0.02)O₂ and the coating layer of0.53Li₂O.0.9NiO_(3/2)0.08CoO_(3/2).0.02AlO_(3/2).SiO₂.

EXAMPLE 22

The positive active material of Example 22 includes a core ofLi_(1.09)Ni_(0.88)Co_(0.10)Al_(0.01)Ti_(0.01)O₂ obtained via sol-gelmethod and 0.80 wt % of coating layer of0.55Li₂O.0.88NiO_(3/2).0.1CoO_(3/2).0.01AlO_(3/2).0.01TiO₂.SiO₂ having athickness of 50˜80 nm.

The method for preparing the positive active material of Example 22includes the steps of:

Dissolving lithium acetate, nickel acetate, cobalt acetate, aluminumnitrate, nano titanium dioxide at an atom ratio of1.11:0.88:0.10:0.01:0.01 in deionized water in a container and obtaininga mixed solution; adding citric acid into the mixed solution afterlithium acetate, nickel acetate, cobalt acetate, aluminum nitrate, nanotitanium dioxide being fully dissolved, the ratio of citric acid to thetotal metal ions is 2:1; stirring the mixed solution in the container ina water bath at 85° C. to evaporate the water and obtain gelatinoussubstance; placing the container in an oven at 160° C. for 5 hours andobtaining brown-black substance; milling the brown-black substance intopowder, sintering the powder in air at 750° C. for 5 hours and obtainingthe core of Li_(1.09)Ni_(0.88)Co_(0.10)Al_(0.01)Ti_(0.01)O₂;

Dispersing the sintered core ofLi_(1.09)Ni_(0.88)Co_(0.10)Al_(0.01)Ti_(0.01)O₂ in 0.3% silicic acidsolution having a concentration of 500 g/L and obtaining a mixedsolution; placing the solution in a water bath of 85° C. to evaporatethe water and obtain gelatinous substance; sintering the gelatinoussubstance in air at 600° C. for 18 hours, and obtaining a positiveactive material including the core ofLi_(1.09)Ni_(0.88)Co_(0.10)Al_(0.01)Ti_(0.01)O₂ and the coating layer of0.55Li₂O.0.88NiO_(3/2).0.1CoO_(3/2).0.01AlO_(3/2).0.01TiO₂.SiO₂.

EXAMPLE 23

The positive active material of Example 23 includes a core ofLi_(0.98)Ni_(0.50)Mn_(0.50)O₂ obtained via solvothermal method and 2.10wt % of coating layer of 0.49Li₂O.0.5NiO.0.5MnO₂.SiO₂ having a thicknessof 80˜100 nm.

The method for preparing the positive active material of Example 23includes the steps of:

Dissolving nickel acetate and manganese acetate at an atom ratio of0.50:0.50 in deionized water in a container and obtaining a mixedsolution; adding sodium persulfate in the mixed solution after nickelacetate and manganese acetate being fully dissolved in the deionizedwater, with the ratio of sodium persulfate to the metal ions being 2:1;placing the container containing mixed solution in a PTFE airtightcontainer, placing the container in a stainless steel housing, andputting the container enclosed by the housing in an oven at 135° C. andreacting for 24 hours; after cooling down, washing the reaction productwith deionized water repeatedly; sintering the mixture of the washedreaction product and LiOH.H₂O in air at 750° C. for 10 hours, andobtaining the core of Li_(0.98)Ni_(0.50)Mn_(0.50)O₂.

Dispersing the sintered core powder of Li_(0.98)Ni_(0.50)Mn_(0.50)O₂ in0.8% orthosilicate solution having a concentration of 500 g/L andobtaining a mixed solution; setting the mixed solution in a water bathof 85° C. to evaporate the water and obtain gelatinous substance;sintering the gelatinous substance in air at 800° C. for 20 hours, andobtaining a positive active material including the core ofLi_(0.98)Ni_(0.50)Mn_(0.50)O₂ and the coating layer of0.49Li₂O.0.5NiO.0.5MnO₂.SiO₂.

EXAMPLE 24

The positive active material of Example 24 includes a core ofLi_(1.07)Ni_(0.80)Mn_(0.20)O₂ obtained via coprecipitation method and0.05 wt % of coating layer of 0.54Li₂O.0.2NiO.0.6NiO_(3/2).0.2MnO₂.SiO₂having a thickness of 100˜150 nm.

The method for preparing the positive active material of Example 24includes the steps of:

Dissolving NiSO₄ and MnSO₄ at an atom ratio of 0.80:0.20 in deionizedwater and obtaining a mixed solution having a concentration of 1 mol/L;adding 1 mol/L NaOH solution into the mixed solution and stirring, andmaintaining the temperature at 75° C.; dripping ammonia into the mixedsolution to control the pH value of the mixed solution at 10.3;obtaining loose coprecipitate after full reaction; washing thecoprecipitate with deionized water and ethanol repeatedly; sintering thewashed coprecipitate in air at 500° C. for 5 hours and obtaining secondparticles consisting of primary particles having an average size of400-600 nm; fully mixing the sintered coprecipitate with LiOH.H₂O andsintering the mixture of the coprecipitate and LiOH.H₂O in air at 750°C. for 10 hours, and obtaining the core ofLi_(1.07)Ni_(0.80)Mn_(0.20)O₂.

Mixing and milling SiO₂ with the core of Li_(1.07)Ni_(0.80)Mn_(0.20)O₂at a mass ratio of 0.0003:1 in a planetary ball mill having a rotationspeed of 300 r/min for 5 hours; sintering the fully milled mixture inair at 750° C. for 10 hours and obtaining a positive active materialincluding the core of Li_(1.07)Ni_(0.80)Mn_(0.20)O₂ and the coatinglayer of 0.54Li₂O.0.2NiO.0.6NiO_(3/2)0.2MnO₂.SiO₂.

EXAMPLE 25

The positive active material of Example 25 includes a core ofLi_(1.04)Ni_(0.85)Mn_(0.12)Al_(0.03)O₂ obtained via sol-gel method and2.50 wt % of coating layer of0.52Li₂O.0.12NiO.0.73NiO_(3/2).0.12MnO₂.0.03AlO_(3/2).SiO₂ having athickness of 20˜40 nm.

The method for preparing the positive active material of Example 25includes the steps of:

Dissolving lithium acetate, nickel acetate, manganese acetate, aluminumnitrate at an atom ratio of 1.07:0.85:0.12:0.03 in deionized water in acontainer and obtaining a mixed solution; adding citric acid into themixed solution after lithium acetate, nickel acetate, manganese acetate,aluminum nitrate being fully dissolved, with the ratio of citric acid tothe total metal ions being 2:1; setting the container having the mixedsolution in a water bath of 85° C. to evaporate the water and obtaingelatinous substance; placing the container in an oven at 160° C. for 5hours, and obtaining brown-black substance; milling the brown-blacksubstance into powder, and sintering the powder in air at 750° C. for 5hours and obtaining the core of Li_(1.04)Ni_(0.85)Mn_(0.12)Al_(0.03)O₂;

Dispersing the sintered core powder ofLi_(1.04)Ni_(0.85)Mn_(0.12)Al_(0.03)O₂ in 0.8% silicic acid solutionhaving a concentration of 500 g/L and obtaining a mixed solution;setting the mixed solution in a water bath of 85° C. to evaporate thewater and obtain gelatinous substance; sintering the gelatinoussubstance in air at 600° C. for 20 hours, and obtaining a positiveactive material including the core ofLi_(1.04)Ni_(0.85)Mn_(0.12)AlO_(0.03)O₂ and the coating layer of0.52Li₂O.0.12NiO.0.73NiO_(3/2).0.12MnO₂.0.03AlO_(3/2).SiO₂.

COMPARATIVE EXAMPLE 1

The positive active material of Comparative Example 1 includes a core ofLi_(1.09)Ni_(0.1)Co_(0.5)Mn_(0.4)O₂ obtained via coprecipitation methodand 0.03 wt % of coating layer of Al₂O₃ having a thickness of 50-100 nm.

The method for preparing the positive active material of ComparativeExample 1 includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 0.1:0.5:0.4 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, and maintaining the temperature at 75° C.; obtaining loosecoprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; sintering the washedcoprecipitate in air at 500° C. for 5 hours; fully mixing the sinteredcoprecipitate with LiOH.H₂O and sintering the mixture of thecoprecipitate and LiOH.H₂O in air at 900° C. for 20 hours, and obtainingthe core of Li_(1.09)Ni_(0.1)Co_(0.5)Mn_(0.4)O₂ consisting of secondaryparticles formed by primary particles having a particle size of 4.0-6.0μm.

Mixing nano Al₂O₃ powder with the core ofLi_(1.09)Ni_(0.1)Co_(0.5)Mn_(0.4)O₂ at a mass ratio of 0.003:0.97;milling the mixture of nano Al₂O₃ powder and the core ofLi_(1.09)Ni_(0.1)Co_(0.5)Mn_(0.4)O₂ in a planetary ball mill having arotation speed of 300 r/min for 5 hours; sintering the fully milledmixture in air at 900° C. for 10 hours and obtaining a positive activematerial including the core of Li_(1.09)Ni_(0.1)Co_(0.5)Mn_(0.4)O₂ the acoating layer of Al₂O₃.

COMPARATIVE EXAMPLE 2

The positive active material of Comparative Example 2 isLi_(1.10)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂ obtained via coprecipitation method.

The method for preparing the positive active material of ComparativeExample 2 includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 1.0:1.0:1.0 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, and maintaining the temperature at 75° C.; obtaining loosecoprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; sintering the washedcoprecipitate in air at 500° C. for 5 hours; fully mixing the sinteredcoprecipitate with LiOH.H₂O and sintering the mixture of thecoprecipitate and LiOH.H₂O in air at 850° C. for 10 hours, and obtainingpositive active material of Li_(1.10)Ni_(1/3)Co_(1/3)Mn_(1/3)O₂consisting of secondary particles formed by primary particles having aparticle size of 0.8-1.0 μm.

COMPARATIVE EXAMPLE 3

The positive active material of Comparative Example 3 isLi_(1.08)Ni_(0.5)Co_(0.2)Mn_(0.3)O₂ obtained via coprecipitation method.

The method for preparing the positive active material of ComparativeExample 3 includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 5.0:2.0:3.0 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, and maintaining the temperature at 75° C.; obtaining loosecoprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; sintering the washedcoprecipitate in air at 500° C. for 5 hours; fully mixing the sinteredcoprecipitate with LiOH.H₂O and sintering the mixture of thecoprecipitate and LiOH.H₂O in air at 800° C. for 10 hours, and obtainingthe positive active material of Li_(1.08)Ni_(0.5)Co_(0.2)Mn_(0.3)O₂.

COMPARATIVE EXAMPLE 4

The positive active material of Comparative Example 4 isLi_(0.98)Ni_(0.6)Co_(0.2)Mn_(0.2)O₂ obtained via sol-gel method.

The method for preparing the positive active material of ComparativeExample 4 includes the steps of:

Dissolving lithium acetate, nickel acetate, cobalt acetate, manganeseacetate at an atom ratio of 0.99:0.60:0.20:0.20 in deionized water in acontainer and obtaining a mixed solution; adding citric acid into themixed solution after lithium acetate, nickel acetate, cobalt acetate,manganese acetate being fully dissolved, with the ratio of citric acidto the total metal ions being 2:1; stirring the mixed solution in thecontainer in a water bath of 85° C. to evaporate the water and obtaingelatinous substance; placing the container in an oven at 160° C. for 5hours, and obtaining brown-black substance; milling the brown-blacksubstance into powder, sintering the powder in air at 750° C. for 10hours and obtaining the positive active material ofLi_(0.98)Ni_(0.6)Co_(0.2)Mn_(0.2)O₂.

COMPARATIVE EXAMPLE 5

The positive active material of Comparative Example 5 includes a core ofLi_(0.9)Ni_(0.75)Co_(0.15)Mn_(0.1)O₂ obtained via coprecipitation methodand 0.05 wt % of coating layer of MgO having a thickness of 10-15 nm.

The method for preparing the positive active material of ComparativeExample 5 includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 0.75:0.15:0.10 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, and maintaining the temperature at 75° C.; obtaining loosecoprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; mixing the washed coprecipitatewith LiOH.H₂O and sintering the mixture of the washed coprecipitate anLiOH.H₂O in air at 700° C. for 5 hours, and obtaining the core ofLi_(0.9)Ni_(0.75)Co_(0.15)Mn_(0.1)O₂ consisting of secondary particlesformed by primary particles having a particle size of 4.0-6.0 μm.

Mixing and milling nano MgO powder with the core ofLi_(0.9)Ni_(0.75)Co_(0.15)Mn_(0.1)O₂ at a mass ratio of 0.0005:1 in aplanetary ball mill having a rotation speed of 500 r/min for 5 hours;sintering the fully milled mixture in air at 900° C. for 10 hours andobtaining a positive active material including the core ofLi_(0.9)Ni_(0.75)Co_(0.15)Mn_(0.1)O₂ and the coating layer of MgO.

COMPARATIVE EXAMPLE 6

The positive active material of Comparative Example 6 isLi_(1.03)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂ obtained via coprecipitation method.

The method for preparing the positive active material of ComparativeExample 6 includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 8.0:1.0:1.0 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, and maintaining the temperature at 75° C.; obtaining loosecoprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; sintering the washedcoprecipitate in air at 500° C. for 5 hours; fully mixing the sinteredcoprecipitate with LiOH.H₂O; sintering the mixture of sinteredcoprecipitate and LiOH.H₂O in air at 900° C. for 8 hours, and obtainingthe positive active material of Li_(1.03)Ni_(0.8)Co_(0.1)Mn_(0.1)O₂consisting of secondary particles formed by primary particles having aparticle size of 0.7-0.8 μm.

COMPARATIVE EXAMPLE 7

The positive active material of Comparative Example 7 includes a core ofLi_(1.07)Ni_(0.82)Co_(0.1)Mn_(0.08)O₂ obtained via coprecipitationmethod and 0.12 wt % of coating layer of AlPO₄ having a thickness of12-15 nm.

The method for preparing the positive active material of ComparativeExample 7 includes the steps of:

Dissolving NiSO₄, CoSO₄, MnSO₄ at an atom ratio of 0.82:0.10:0.08 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, and maintaining the temperature at 75° C.; obtaining loosecoprecipitate after full reaction; washing the coprecipitate withdeionized water and ethanol repeatedly; mixing the washed coprecipitatewith LiOH.H₂O and sintering the mixture of the washed coprecipitate andLiOH.H₂O in air at 700° C. for 5 hours, and obtaining the core ofLi_(1.07)Ni_(0.82)Co_(0.1)Mn_(0.08)O₂.

Mixing and milling nano AlPO₄ powder with the core ofLi_(1.07)Ni_(0.82)Co_(0.1)Mn_(0.08)O₂ at a mass ratio of 0.0012:1 in aplanetary ball mill having a rotation speed of 300 r/min for 5 hours;sintering the fully milled mixture in air at 800° C. for hours andobtaining a positive active material including the core ofLi_(1.07)Ni_(0.82)Co_(0.1)Mn_(0.08)O₂ and the coating layer of AlPO₄.

COMPARATIVE EXAMPLE 8

The positive active material of Comparative Example 8 isLi_(0.95)Ni_(0.9)Co_(0.05)Mn_(0.05)O₂.

The method for preparing the positive active material of ComparativeExample 8 includes the steps of:

Mixing Li₂CO₃, nickel oxalate, cobalt oxalate, MnCO₃ at a molar ratio of0.49:0.90:0.05:0.05 in a zirconia sander having a rotation speed of 1000r/min for 5 hours, the diameter of the zirconia milling media is 5 mm,and the ratio of zirconia milling media to the mixture of Li₂CO₃, nickeloxalate, cobalt oxalate, MnCO₃ is 1:2; removing the zirconia millingmedia and sintering the remaining mixture in air at 950° C. for 24 hoursand obtaining the positive active material ofLi_(0.95)Ni_(0.9)Co_(0.05)Mn_(0.05)O₂.

COMPARATIVE EXAMPLE 9

The positive active material of Comparative Example 9 is Li_(1.05)CoO₂obtained via coprecipitation method.

The method for preparing the positive active material of ComparativeExample 9 includes the steps of:

Preparing 1 mol/L CoSO₄ solution; slowly dripping 1 mol/L NH₄HCO₃solution at a dripping rate of 1 L/h into the CoSO₄ solution; aftercoprecipitation, filtering and washing the coprecipite with deionizedwater and obtaining CoCO₃ after drying; mixing Li₂CO₃ and CoCO₃ at amolar ratio of 1.07:1 in a planetary ball mill having a rotation speedof 200 r/min for 5 hours; sintering the fully mixed mixture of Li₂CO₃and CoCO₃ in air at 900° C. for 10 hours, and obtaining the positiveactive material Li_(1.05)CoO₂.

COMPARATIVE EXAMPLE 10

The positive active material of Comparative Example 10 isLi_(1.01)Co_(0.89)Mg_(0.05)Al_(0.04)Ti_(0.02)O₂ obtained via sol-gelmethod.

The method for preparing the positive active material of ComparativeExample 10 includes the steps of:

Dissolving lithium acetate, cobalt acetate, nano magnesia, nano alumina,nano titanium dioxide at an atom ratio of 1.03:0.89:0.05:0.04:0.02 indeionized water in a container and obtaining a mixed solution; addingcitric acid into the mixed solution after lithium acetate, cobaltacetate, nano magnesia, nano alumina, nano titanium dioxide being fullydissolved, the ratio of citric acid to the total metal ions is 2:1;stirring the solution in the container in a water bath of 85° C. toevaporate the water and obtain gelatinous substance; placing thecontainer in an oven at 160° C. for 5 hours, and obtaining brown-blacksubstance; milling the brown-black substance into powder, sintering thepowder in air at 900° C. for 24 hours and obtaining the positive activematerial of Li_(1.01)Co_(0.89)Mg_(0.05)Al_(0.04)Ti_(0.02)O₂.

COMPARATIVE EXAMPLE 11

The positive active material of Comparative Example 11 isLi_(0.98)Co_(0.98)Ti_(0.02)O₂ obtained via coprecipitation methodconsisting of monocrystalline particles.

The method for preparing the positive active material of ComparativeExample 11 includes the steps of:

Preparing 1 mol/L CoSO₄ solution; slowly dripping 1 mol/L NH₄HCO₃solution at a dripping rate of 1 L/h into the CoSO₄ solution; aftercoprecipitation, filtering and washing the coprecipitate with thedeionized water, and obtaining CoCO₃ after drying; mixing Li₂CO₃, CoCO₃and TiO₂ at a molar ratio of 1.01:0.98:0.02 in a planetary ball millhaving a rotation speed of 200 r/min for 5 hours; sintering the fullymixed mixture of Li₂CO₃, CoCO₃ and TiO₂ in air at 800° C. for 18 hours,and obtaining the positive active material ofLi_(0.98)Co_(0.98)Ti_(0.02)O₂.

COMPARATIVE EXAMPLE 12

The positive active material of Comparative Example 12 isLi_(1.02)Ni_(0.85)Co_(0.10)Al_(0.05)O₂ obtained via coprecipitationmethod.

The method for preparing the positive active material of ComparativeExample 12 includes the steps of:

Dissolving NiSO₄, CoSO₄, Al(NO₃)₃ at an atom ratio of 0.85:0.10:0.05 indeionized water and obtaining a mixed solution having a concentration of1 mol/L; adding 1 mol/L NaOH solution into the mixed solution andstirring, and maintaining the temperature at 75° C.; dripping ammonia inthe mixed solution to control the pH value of the mixed solution at10.6; obtaining loose coprecipitate after full reaction; washing thecoprecipitate with deionized water and ethanol repeatedly; sintering thewashed coprecipitate in air at 500° C. for 5 hours; mixing the sinteredcoprecipitate with LiOH.H₂O and sintering the mixture of the sinteredcoprecipitate and LiOH.H₂O in air at 750° C. for 10 hours, and obtainingthe positive active material of Li_(1.02)Ni_(0.85)Co_(0.10)Al_(0.05)O₂.

COMPARATIVE EXAMPLE 13

The positive active material of Comparative Example 13 isLi_(1.05)Ni_(0.90)Co_(0.08)Al_(0.02)O₂ obtained via sol-gel method.

The method for preparing the positive active material of ComparativeExample 13 includes the steps of:

Dissolving lithium acetate, nickel acetate, cobalt acetate, aluminumnitrate at an atom ratio of 1.09:0.90:0.08:0.02 in deionized water in acontainer and obtaining a mixed solution; adding citric acid into themixed solution after lithium acetate, nickel acetate, cobalt acetate,aluminum nitrate being fully dissolved, the ratio of the citric acid tothe total metal ions is 2:1; stirring the mixed solution in thecontainer in a water bath of 85° C. to evaporate the water and obtaingelatinous substance; placing the container in an oven at 160° C. for 5hours, and obtaining brown-black substance; milling the brown-blacksubstance into powder, sintering the powder in air at 750° C. for 5hours and obtaining the positive active material ofLi_(1.05)Ni_(0.90)Co_(0.08)Al_(0.02)O₂.

COMPARATIVE EXAMPLE 14

The positive active material of Comparative Example 14 isLi_(1.09)Ni_(0.88)Co_(0.10)Al_(0.01)Ti_(0.01)O₂ obtained via sol-gelmethod.

The method for preparing the positive active material of ComparativeExample 14 includes the steps of:

Dissolving lithium acetate, nickel acetate, cobalt acetate, aluminumnitrate, nano titanium dioxide at an atom ratio of1.11:0.88:0.10:0.01:0.01 in deionized water in a container and obtaininga mixed solution; adding citric acid into the mixed solution afterlithium acetate, nickel acetate, cobalt acetate, aluminum nitrate, nanotitanium dioxide being fully dissolved, the ratio of the citric acid tothe total metal ions is 2:1; stirring the mixed solution in thecontainer in a water bath of 85° C. to evaporate the water and obtaingelatinous substance; placing the container the gelatinous substance inan oven at 160° C. for 5 hours, and obtaining brown-black substance;milling the brown-black substance into powder, sintering the powder inair at 750° C. for 5 hours and obtaining the positive active material ofLi_(1.09)Ni_(0.88)Co_(0.10)Al_(0.01)Ti_(0.01)O₂.

COMPARATIVE EXAMPLE 15

The positive active material of Comparative Example 15 isLi_(0.98)Ni_(0.50)Mn_(0.50)O₂ obtained via sol-gel method.

The method for preparing the positive active material of ComparativeExample 15 includes the steps of:

Dissolving lithium acetate, nickel acetate, manganese acetate at an atomratio of 1.02:0.50:0.50 in deionized water in a container and obtaininga mixed solution; adding citric acid into the mixed solution afterlithium acetate, nickel acetate, manganese acetate being fullydissolved, the ratio of the citric acid to the total metal ions is 2:1;stirring the mixed solution in the container in a water bath of 85° C.to evaporate the water and obtain gelatinous substance; placing thecontainer having the gelatinous substance in an oven at 160° C. for 5hours, and obtaining brown-black substance; milling the brown-blacksubstance into powder, sintering the powder in air at 750° C. for 5hours and obtaining the positive active material ofLi_(0.98)Ni_(0.50)Mn_(0.50)O₂.

COMPARATIVE EXAMPLE 16

The positive active material of Comparative Example 16 isLi_(1.07)Ni_(0.80)Mn_(0.20)O₂ obtained via coprecipitation method.

The method for preparing the positive active material of ComparativeExample 16 includes the steps of:

Dissolving NiSO₄, MnSO₄ at an atom ratio of 0.80:0.20 in deionized waterand obtaining a mixed solution having a concentration of 1 mol/L; adding1 mol/L NaOH solution into the mixed solution and stirring, andmaintaining the temperature at 75° C.; dripping ammonia in the mixedsolution to control the pH value of the mixed solution at 10.3;obtaining loose coprecipitate after full reaction; washing thecoprecipitate with deionized water and ethanol repeatedly; sintering thewashed coprecipitate in air at 500° C. for 5 hours; fully mixing thesintered coprecipitate and LiOH.H₂O; sintering the mixture of thesintered coprecipitate and LiOH.H₂O in air at 750° C. for 10 hours, andobtaining the positive active material of Li_(1.07)Ni_(0.80)Mn_(0.20)O₂.

COMPARATIVE EXAMPLE 17

The positive active material of Comparative Example 17 isLi_(1.04)Ni_(0.85)Mn_(0.12)Al_(0.03)O₂ obtained via sol-gel method.

The method for preparing the positive active material of ComparativeExample 17 includes the steps of:

Dissolving lithium acetate, nickel acetate, manganese acetate, aluminumnitrate at an atom ratio of 1.07:0.85:0.12:0.03 in deionized water in acontainer and obtaining a mixed solution; adding citric acid into themixed solution after lithium acetate, nickel acetate, manganese acetate,aluminum nitrate being fully dissolved, the ratio of the citric acid tothe total metal ions is 2:1; stirring the mixed solution in thecontainer in a water bath of 85° C. to evaporate the water and obtaingelatinous substance; placing the container having the gelatinoussubstance in an oven at 160° C. for 5 hours, and obtaining brown-blacksubstance; milling the brown-black substance into powder, sintering thepowder in air at 750° C. for 5 hours and obtaining the positive activematerial of Li_(1.04)Ni_(0.85)Mn_(0.12)Al_(0.03)O₂.

PREPARATION OF LITHIUM ION BATTERIES

The positive active materials according to Examples 1 to 25, ComparativeExamples 1 to 17 are adopted as positive active materials to manufacturelithium ion batteries via same process, to analyze the electrochemicalperformance of lithium-containing transition metal oxides. The methodfor preparing lithium ion batteries includes the following steps.

The positive active materials according to Examples 1 to 25, ComparativeExamples 1 to 17 are adopted as the positive active materials of thepositive plates, respectively. Artificial graphite is adopted asnegative active material of the negative plate. The positive plate, thenegative plate and the separator are winded to form a secondary lithiumbattery after soldering terminal, packaging the aluminum foil, fillingelectrolyte and pumping the air. The discharge cut-off voltage of eachsecondary lithium battery is 2.80 V. The charge cut-off voltage of eachsecondary lithium battery is 4.50 V (relative to the electric potentialof lithium 4.55 V). The design capacity of each secondary lithiumbattery is 2500 mAh.

PERFORMANCE ANALYSIS

The performances of lithium ion batteries according to Examples 1 to 25and Comparative Examples 1 to 17 are assessed and shown in Table 1.

1. Cycling performance: Each secondary lithium battery is charged at aconstant current of 0.5 C (1225 mA) at 25° C. until the voltage reaches4.50 V. Each secondary lithium battery is then charged at a constantvoltage of 4.50 V until the current reaches 0.05 C (123 mA). Eachsecondary lithium battery is further discharged at a current of 0.5 C(1225 mA) until the voltage reaches 2.80 V. The charging and dischargingcycle is repeated for 1000 times. The discharge capacity of the firstcycle and the discharge capacity of the 1000th cycle are determined. Thecapacity retention rate of each secondary lithium battery is calculatedaccording to the following formula:The capacity retention rate=(discharge capacity of the 1000thcycle/discharge capacity of the first cycle)×100%

2. High temperature storage performance: Each secondary lithium batteryis charged at a constant current of 0.5 C (1225 mA) at 25° C. until thevoltage reaches 4.50V. Each secondary lithium battery is charged at aconstant voltage of 4.50 V until the current reaches 0.05 C (123 mA).The thickness of each secondary lithium battery prior to storage and thefirst discharge capacity is determined. Each fully charged secondarylithium battery is stored in an oven at 60° C. for 100 days. Thethickness of each secondary lithium battery after storage is determined.The expansion rate of each secondary lithium battery after storage iscalculated. Each stored secondary lithium battery is charged at aconstant current of 0.5 C (1225 mA) until the voltage reaches 4.50 V.Each secondary lithium battery is charged at a constant voltage of 4.50V until the current reaches 0.05 C (123 mA). Each secondary lithiumbattery is discharged at a constant current of 0.5 C (1225 mA) until thevoltage reaches 2.80 V. The charge and discharge cycle is repeated forfive cycles. The final discharge capacity is recorded. The capacityretention rate relative to the first discharge capacity is calculatedaccording to the following formula.Expansion rate of a stored secondary lithium battery=(thickness of astored secondary lithium battery thickness of a secondary lithiumbattery prior to storage)/ thickness of a secondary lithium batteryprior to storage×100%.Capacity retention rate of a stored secondary lithium battery=(dischargecapacity after 100 days storage)/(discharge capacity of the firstcycle)×100%.

3. Safety performance test: Each secondary lithium battery is charged ata constant current of 0.5 C (1225 mA) at 25° C. until the voltagereaches 4.50 V. Each secondary lithium battery is charged at a constantvoltage of 4.50 V until the current reaches 0.05 C (123 mA). Eachsecondary lithium battery is disassembled in a glovebox full of Argon.The positive plate of each secondary lithium battery is taken out andwashed in DMC solution. After the DMC has completely evaporated, thepositive active material is scratched from the positive plate. 10 mgscratched positive active material of each secondary lithium battery isput in an aluminum crucible. The aluminum crucible is sealed after 0.1μL electrolyte has been added. The scanning temperature of the DSC testis 50˜500° C. and the heating rate is 10° C./min.

TABLE 1 Performance Test Results of lithium ion batteries according toExamples and Comparative Examples Capacity retention Capacity rate ofExpansion retention second rate of rate of a lithium stored storedMaximum battery second second DSC after lithium lithium DSC heatExothermic cycling battery battery release (J/g) peak (□) Example 183.40%  4.60% 87.20% 651 299 Example 2 91.70%  5.10% 87.10% 641 321Example 3 82.30%  7.30% 83.10% 793 311 Example 4 90.40%  2.70% 89.10%802 308 Example 5 76.20% 11.50% 86.10% 810 260 Example 6 83.15%  4.60%87.00% 821 271 Example 7 81.40%  9.20% 81.30% 891 247 Example 8 80.10%11.95% 81.20% 893 257 Example 9 70.20%  4.20% 76.10% 951 226 Example 1086.20%  3.25% 90.10% 630 336 Example 11 84.30%  4.25% 86.80% 810 309Example 12 85.90%  2.60% 89.90% 768 312 Example 13 81.90%  6.20% 84.30%782 277 Example 14 95.70%  1.20% 94.10% 620 327 Example 15 84.40%  3.90%87.60% 930 249 Example 16 85.30%  4.05% 89.80% 910 254 Example 17 73.10%10.10% 82.40% 1231 245 Example 18 79.30% 15.60% 79.40% 1160 239 Example19 77.90% 11.10% 85.10% 1210 242 Example 20 64.70% 14.30% 89.20% 921 234Example 21 74.80% 14.10% 76.30% 861 231 Example 22 75.40% 11.40% 84.50%1127 234 Example 23 80.30%  8.10% 91.40% 731 282 Example 24 89.10%15.30% 85.00% 810 247 Example 25 75.20% 15.30% 87.20% 870 259Comparative Example 1 78.10%  5.10% 81.00% 693 295 Comparative Example 275.30%  7.30% 84.20% 657 315 Comparative Example 3 65.70% 12.20% 73.80%851 290 Comparative Example 4 52.20% 23.60% 65.20% 860 270 ComparativeExample 5 61.20%  12.2% 67.50% 852 266 Comparative Example 6 56.80%30.70% 65.70% 971 232 Comparative Example 7 58.10% 25.10% 71.30% 954 238Comparative Example 8 55.60% 20.50% 63.50% 1052 211 Comparative Example9 60.40% 25.70% 52.30% 1391 214 Comparative Example 10 65.00% 32.70%41.20% 1379 222 Comparative Example 11 42.00% 28.90% 35.00% 1381 221Comparative Example 12 56.70% 29.00% 70.60% 1161 216 Comparative Example13 68.00% 38.10% 72.90% 1263 221 Comparative Example 14 69.30% 24.40%70.60% 1345 203 Comparative Example 15 72.20% 18.60% 70.00% 862 262Comparative Example 16 70.10% 19.80% 70.80% 970 212 Comparative Example17 68.40% 33.20% 50.30% 1051 221

It is clearly shown in Table 1 that:

1) The positive active material having a core of lithium transitionmetal oxide and a coating layer according to the present invention hasremarkably improved charge-discharge cycle performance at 2.80 V˜4.50 V.Comparing Examples 1 to 25 and Comparative Examples 1 to 17, after 1000cycles, the positive active material having a core of lithium transitionmetal oxide and a coating layer according to the present invention has ahigher capacity retention rate than that of ordinary lithium transitionmetal oxide positive active material. The positive active materialhaving a core of lithium transition metal oxide and a coating layer hasdesirable cycling performance, especially the cycling performance athigh voltage of 4.50 V, because the coating layer can stabilize the coreand prevent phase change.

2) The positive active material having a core of lithium transitionmetal oxide and a coating layer according to the present invention hasremarkably improved high temperature storage performance at 4.50 V.Comparing Examples 1 to 25 and Comparative Examples 1 to 17, thepositive active material having a core of lithium transition metal oxideand a coating layer according to the present invention has a much lowerthickness expansion rate after charged to 4.50 v and stored at 60° C.for 100 days than that of ordinary lithium transition metal oxidepositive active material. The positive active material having a core oflithium transition metal oxide and a coating layer of the presentinvention has desirable cycling performance The high temperature storageperformance at 4.50 v is improved remarkably, because the coating layerhas higher chemical stability and higher electrochemical stability,which can remarkably reduce the catalytic activity of the positiveactive material.

3) The positive active material having a core of lithium transitionlithium transition metal oxide and a coating layer according to thepresent invention has remarkably improved safety performance at 4.50 V.Comparing Examples 1 to 25 and Comparative Examples 1 to 17, when thesecondary lithium battery using the positive active material having acore of lithium transition metal oxide and a coating layer according tothe present invention is charged to 4.55 V, DSC exotherm of thesecondary lithium battery is much less than that of a secondary lithiumbattery using ordinary lithium transition metal oxide positive activematerial. Silicate has stable crystal structure. The coating layer ofsilicate can improve the thermal stability of the positive activematerial and the safety performance of the secondary lithium battery.The coating layer in situ formed on the core can effectively eliminatethe sites having high reactivity on the surface of the core, reduce thecatalytic activity of the final product in the secondary lithium batteryand, therefore, obtain stable positive active material.

Summarizing the above, the positive active material and method forpreparing the same according to the present invention have the followingadvantages.

Firstly, the coating layer can conduct lithium ions. Compared with othercoating layer of oxide, the coating layer according to the presentinvention has higher lithium-ion conductivity.

Secondly, the coating layer has stable chemical stability andelectrochemical stability. Even after being charged to 4.70 V, theskeleton of silica-oxygen structure still can protect the core, whichwill remarkably reduce the catalytic activity of the core and improvethe chemical stability of the positive active material. In addition, thesilicate has stable crystal structure. The coating layer of silicate canimprove the thermal stability of the positive active material, therebyimproving the safety performance of the secondary lithium battery.

Thirdly, the coating layer is in-situ formed on the core. Part of thecoating layer comes from the core. Therefore, the coating layer can beuniformly formed on the core.

Fourthly, the coating layer is apt to be formed on the sites having highreactivity of the core. The method according to the present inventioncan effectively eliminate the sites having high reactivity on thesurface of the core, thereby reducing the catalytic activity of thefinal product in the secondary lithium battery and obtaining stablepositive active material.

Fifthly, the method according to the present invention can reduce theoxidizing ability of the core in charging state. The M⁴⁺ having strongoxidizing ability on the surface of the core is coated by the coatinglayer and cannot contact the electrolyte. Therefore, the M⁴⁺ can hardlyoxidize and decompose the electrolyte.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Moreover, although the foregoing descriptions and the associateddrawings describe example embodiments, it should be appreciated thatalternative embodiments without departing from the scope of the appendedclaims. Although specific terms are employed herein, they are used in ageneric and descriptive sense only and not for purposes of limitation.

What is claimed is:
 1. A positive active material for a secondarylithium battery, comprising: a core of lithium transition metal oxiderepresented by Formula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β) and a coatinglayer of lithium transition metal silicate represented by Formulax′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) which in-situ formed on the core,wherein element represented by M is at least one of Ni, Co and Mn;element represented by N and N′ each is at least one of Na, K, Rb, Cs,Be, Mg, Ca, Sr, Ba, Ra, Al, Ga, In, Ge, Sn, Sc, Ti, B, V, Cr, Mn, Fe,Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, W, Ru, Rh, Pd, Ag, Cd, La, Ce, Pr, Nd,Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu; element represented by A and Beach is at least one of N, F, P, 5, Cl, Se; and 0.8≤x≤1.3, 0.6≤y≤1.0,0.01≤x′≤2.1, 0.2≤y′≤1.5, 0.1≤a≤3.0, 0≤α≤0.2, 0≤β≤0.4, 0≤λ≤0.5, 0≤ζ≤0.5.2. The positive active material of claim 1, wherein in the lithiumtransition metal oxide represented by FormulaLi_(x)M_(y)N_(1-y)O_(2-α)A_(β), the element represented by M iscombination of elements Ni, Co, Mn; and the element represented by N isat least one of Mg, Al, Ti, B, V, Mo, W, Ni, Co, Mn, Y, Ce; 0.7≤y≤1.0.3. The positive active material of claim 2, wherein the elementrepresented by M in the lithium transition metal oxide represented byFormula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β) is Co, Ni_(0.5)Co_(0.5),Ni_(0.7)Co_(0.3), Ni_(0.8)Co_(0.2), Ni_(0.9)Co_(0.1),Ni_(1/3)Co_(1/3)Mn_(1/3), Ni_(0.5)Co_(0.2)Mn_(0.3),Ni_(0.6)Co_(0.2)Mn_(0.2), Ni_(0.8)Co_(0.01)Mn_(0.1) or combinationsthereof.
 4. The positive active material of claim 1, wherein the elementrepresented by N in Formula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β) is at leastone of Mg, Al, Ti, B, Mo, Zr, V, Ce, W, and 0.95≤y≤1.0.
 5. The positiveactive material of claim 1, wherein the element represented by A in thelithium transition metal oxide represented by FormulaLi_(x)M_(y)N_(1-y)O_(2-α)A_(β) is N and/or F, and 0≤β≤0.1.
 6. Thepositive active material of claim 1, wherein the element represented byB in the lithium transition metal silicate represented by Formulax′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) is N and/or F, and 0≤ζ≤0.2.
 7. Thepositive active material of claim 1, wherein in the lithium transitionmetal silicate represented by Formula x′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ),0.1≤x′≤1, 0.2≤y′≤1.0.
 8. The positive active material of claim 1,wherein the coating layer of lithium transition metal silicaterepresented by Formula x′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) isLi₂O.N′O.SiO_(2-λ)B_(ζ),0.5Li₂O.N′O_(1.5).Si_(2-λ)B_(ζ),Li₂O.N′O₂.SiO_(2-λ)B_(ζ) or combinationsthereof.
 9. The positive active material of claim 1, wherein the weightcontent of the coating layer of lithium transition metal silicaterepresented by Formula x′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) in the positiveactive material is 0.01%-30%.
 10. A secondary lithium battery,comprising a positive electrode, a negative electrode and a separatorbetween the positive electrode and the negative electrode, wherein thepositive electrode comprises the positive active material of claim 1.11. The positive active material of claim 1, wherein in the lithiumtransition metal oxide represented by FormulaLi^(x)M_(y)N_(1-y)O_(2-α)A_(β),the element represented by M is one ortwo of Ni, Co, and the element represented by N is one or more of theMg, Al, Ti, B, V, Mo, W, Ni, Co, Mn, Y, Ce; 0.7≤y≤1.0.
 12. The positiveactive material of claim 1, wherein the element represented by N inFormula Li_(x)M_(y)N_(1-y)O_(2-α)A_(β) is at least one of Mg, Al, Ti, B,Mo, Zr, V, Ce, W, and 0.99≤y≤1.0.
 13. The positive active material ofclaim 1, wherein the weight content of the coating layer of the lithiumtransition metal silicate represented by Formulax′Li₂O.y′N′O_(a).SiO_(2-λ)B_(ζ) in the positive active material is0.01%-5.0%.